Device for guiding light

ABSTRACT

Described is a device for guiding light consisting of at least one partially translucent surface material, with a surface upper side, which has optically active surface structures for guiding and/or scattering light, as well as an optically switchable coating provided at least in partial areas of the surface structures, or at least two directly or indirectly opposing surface upper sides, of which one exhibits optically active surface structures for guiding and/or scattering light, and the other provides an optically switchable coating that covers at least parts of the surface upper side.

TECHNICAL AREA

The invention relates to a device for guiding light consisting of atleast one partially translucent surface material.

PRIOR ART

Modern buildings increasingly exhibit large, glazed surfaces, as aresult of which the incident sunlight reduces thermal energy demandduring the heating period, and increased daylight exposure improveslighting in buildings. At the same time, however, undesired effects canbe encountered, in particular overheating in the buildings on warm days,or glare caused by direct sunlight, e.g., at display workstations.

These problems are presently being countered through the use of staticelements, e.g., tinted glazing with low solar transmission, porches withan awning or balcony in front of window surfaces, etc. Opticallyswitchable elements, e.g., mechanically adjustable shading systems inthe form of shades or Austrian blinds, or more recently, opticallyswitchable windows, such as electrochromic or gasochromic windows, areable to counter overheating and unpleasant glare effects. Electrochromicsystems are described, for example, in C. G. Granqvist, “Handbook ofinorganic electrochromic materials”, Elsevier Amsterdam (1995), or“Electrochromism”, P. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCHWeinheim (1995). Electrochromic systems are related to so-calledgasochromic systems, whose optical properties change through reactionwith a gas, and which are also described, among other places, in DE 4440 572 and EP 0 792 406 B1, or in “Mechanism of the gasochromiccoloration of porous WO₃ films”, Solid State Ionics, Volume 127, Issues34, Jan. 2, 2000, pp. 319-328, A. Georg, W. Graf, R. Neumann and V.Wittwer.

Also known from DE 38 22 796 A1 is a device and method for changing thelight permeability of windowpanes, in particular dual-glazedwindowpanes. In this case, an electrochromic material is incorporatedbetween two glass panes, and changes its transmission properties duringexposure to an electric voltage. In a particularly highlightedembodiment, numerous liquid crystal surface fields arranged in a matrixare provided between two glass panes, which are individually subjectedto an electrical current, thereby making it possible to tint awindowpane with such a structural design in individual surface areas.However, light is not guided with this system.

Optically switchable systems have known materials that change theirrefractive index, optical activity, e.g., by rotating the polarizationplane in liquid crystals, or alter their absorption index, to in thisway induce adjustable absorption actions. The latter materials arereferred to as electrochromic, gasochromic, phototropic/photochromic orphotoelectrochromic materials, depending on the type of influence theyexert. Also known are materials that undergo a transformation from adielectric to metallic state, e.g., in metal hydride mirrors (e.g., see“Toward solid-state switchable mirrors using a zirconium oxide protonconductor”, Solid State Ionics, Volume 145, Issues-1-4, Dec. 1, 2001,pp. 17-24, Virginie M. M. Mercier and Paul van der Sluis, “Cyclingdurability of switchable mirrors”, Electrochimica Acta, Volume 46,Issues 13-14, Apr. 2, 2001, pp. 2173-2178, Anna-Maria Janner, Paul vander Sluis and Virginie Mercier).

By contrast, static elements bring about a lasting reduction in overallincident light, e.g., through window openings, in a desired fashion notjust during warm times of the year, but also during wintertime, therebydiminishing the desired contribution of sunlight to heating a roomduring cold times of the year. On the other hand, mechanicallyadjustable systems enable a largely individual adjustment of shadinglevel to the given light conditions, but such systems are often complex,expensive and also maintenance intensive.

One approach to avoiding glare effects inside of rooms involves thetargeted guiding of direct sunlight into solid angle areas where nodiscernible glare can arise, e.g., toward the ceiling of an interiorspace. Optical elements that work based on optical refraction,reflection and/or internal total reflection are used for this purpose.Such optical elements are typically designed as light-transparentsurface elements, whose surfaces, for example, have prismatic structuresthat transmit, divert, scatter or reflect the incident rays, dependingon the angle of incidence. In the case of permanently installed surfaceelements of this kind, the seasonal variance in solar altitude causesdirect sunlight to be specifically reflected over a specific period oftime, e.g., during the summer months, while allowing it to pass throughthe light guiding system nearly unimpeded for the remaining time.

Another system for guiding light consists of complementary structuresmakes use of the fact that only a minimally small parallel ray shifttakes place during passage through a thin, plane-parallel gap. As aresult, an element that performs a shading function based on totalreflection at specific angles of incidence can be provided withtransparent properties by adding a complementary structure to theelement. Such systems are known, for example, from DE 17 40 553, DE 1171 370, U.S. Pat. No. 2,976,759, U.S. Pat. No. 3,393,034, U.S. Pat. No.4,148,563, U.S. Pat. No. 4,519,675, U.S. Pat. No. 5,880,886, DE 195 42832 A1 or DE 196 22 670.

In addition, the function of light-guiding prisms can be furtherexpanded by making the prisms movable, so that the alignment of therespective prism surfaces relative to the light source can bespecifically varied. Such systems are known from DE 1 497 348, DE 31 38262 A1, U.S. Pat. No. 4,773,733, DE 195 42 832 A1 or DE 197 00 111 A1,in which structured lamellae or prism rods are pivoted around anessentially horizontal axis, as a result of which the light-guidingstructures can be specifically aligned or made to follow the sun.However, the disadvantages associated with lamellar shades or Australianblinds apply to these movable systems, namely high procurement costs andsusceptibility to disruption owing to mechanical failure.

Therefore, prior art does describe measures to avoid overheating inbuildings, e.g., optically switchable windows, along with methods toavoid glare caused by guiding light, e.g., using prismaticallystructured geometries.

However, the requirements that would have to be placed on reducing thetransmission of an optically switchable window to avoid glare are verystringent, so that corresponding windows are not available or veryexpensive to manufacture, and also exhibit additional disadvantagesduring operation, such as longer switching times, lower transmission inthe decolored state, or lower long-term stability. At the same time,however, suppressing glare in this way would also diminish the desiredeffect of reducing heating energy, in particular in winter.

By contrast, known light guiding devices able to prevent glare onlynegligibly help to avoid overheating on warm days, if at all, especiallysince they are in most cases limited to deflecting direct sunlight, andhence cannot effectively mask diffuse sky light.

Static coatings in conjunction with such light guiding devices canmarkedly reduce overheating in warm periods of the year through backreflection, light scattering or absorption. However, these maskingmechanisms only make it possible to utilize a slight portion of solarenergy for heating a room during the cold time of year.

One special disadvantage to optical devices for geometric light guidingrelates to the unavoidable, manufacturing-related deviations of actuallight guiding structures from the ideal structure. In particular cornersare rounded in reality. These rounded areas result in undesired glareeffects, in particular when looking directly at the window.

EXPLANATION OF THE INVENTION

The object of the invention is to further develop a device for guidinglight out of at least one partially translucent surface material,preferably designed as a window element or integratable into one, insuch a way that the device avoids the disadvantages specified above inprior art. In particular, the object is to indicate a light guidingdevice that combines all advantages described above for the respectiveindividual light deflection systems. In particular, the light guidingdevice according to the invention is intended to avoid all instances ofglare caused by the direct incidence of sunlight inside a room, or bymanufacturing-related rounded areas on corners of surface structures,and beyond that to ensure effective protection against overheating, inparticular during warm times of the year. At the same time, the goal isto meet the requirement of allowing enough light inside a room whileeffectively suppressing any danger of glare, primarily in cold times ofthe year. In addition, the object is to indicate a light guiding elementwith optical properties having a high optical selectivity andfunctionality, i.e., to enable light deflection with an exceedingly highangular selectivity relative to the angle of incidence of the sunlighton the device. Finally, the object is to keep manufacturing-relatedcosts as low as possible, thereby yielding an economically interestingproduct that is also suitable above all for applications involving largesurface areas.

The object of the invention is resolved as specified in claims 1 and 4.The subclaims relate to features that advantageously further develop theinventive idea. Also indicated is a method according to the inventionfor manufacturing the light-deflecting devices.

The first solution according to the invention provides for alight-guiding device consisting of at least one partially translucentsurface material, with at least one surface upper side, which hasoptically active surface structures for guiding and/or scattering light.

In this conjunction, the words “at least partially translucent” areintended to denote a type of material that can be exposed to solarradiation from the visible spectral region with little or notransmission losses.

In a broader sense, this also applies to those spectral regionsimmediately bordering the visible spectral region at shorter andespecially longer wavelengths.

Also provided at least in partial areas of the surface structures is anoptically switchable coating, which covers the surface structuresentirely, or only in limited partial areas, preferably along edgeprogressions, depending on user requirements.

As an alternative to directly coating the surface structures with theoptically switchable layer, a second surface upper side situatedopposite, preferably parallel to, the surface upper side provided withthe surface structures can be provided with an optically switchablelayer, at least in partial areas. The second surface upper side caneither be separated from the first surface upper side, e.g., by twoseparate surface materials, or connected as a single piece with thefirst surface upper side, e.g., in the form of a front and back side ofa surface material designed as a windowpane.

In a simplest embodiment of the device according to the invention, thestructured surface upper side of a known optical light guiding surfaceelement is provided with an optically switchable layer. This combinationadvantageously merges the advantages of classic light-guiding orscattering optical surface elements with those optically switchablesystems described in the introduction to the specification, therebysuppressing glare effects on the one hand, and avoiding overheatingeffects during warm times of the year on the other. This makes itpossible to effectively suppress the danger of glare even during coldtimes of the year, while the solar radiation flux penetrating into aroom markedly helps to warm up interior spaces given a correspondingincrease in transmission of the optically switchable layer. Thedisadvantages described for individual systems are not encountered inthe device according to the invention. The manufacturing-related glarestrips along rounded corner passages of the light-guiding surfacestructures are locally diminished in terms of their glare effect by thelight-absorbing layer by providing the optically switchable layer withan elevated glare effect on the surface structures, preferably onprecisely those surface areas.

The term “optically active surface structures” primarily encompassesstructural geometries that provide optically active interfaces, at whichlight is refracted, reflected or scattered according to the laws ofgeometric optics as it passes through. This applies to macroscopicstructural elements whose structural dimensions indeed have interfacesin the centimeter and decimeter range. Cracks, gaps or slits in thesurface upper side of a surface material, e.g., a glass pane, typicallyalready represent such surface structures at whose interfaces rays oflight are deflected as a function of the respective interfaceinclinations relative to the incident light. In like manner, however,three dimensional structures raised from the surface upper side, such asprisms, squares, pyramids, lens bodies, etc. also represent suitablesurface structures that can be combined according to the invention withswitchable coatings. Finally, it is also conceivable to form cavities bydirectly linking two flat materials with a corresponding surfacestructure, which also incorporate interfaces and deflect light. However,the above term “optically active surface structures” is also intended toinclude optically active microstructures whose optical deflectioncapacity cannot be exclusively described by the laws of geometricoptics. Also conceivable are combinations of the macro andmicrostructures mentioned at the outset.

As will be explained in detail below, the targeted light guiding deviceconsisting of at least one partially translucent surface material can beused in a particularly advantageous manner as a window element or partof a window element, preferably for buildings, but also in specificinstances for other locations, e.g., vehicles like ships, cars andplanes. Also conceivable is use in display elements, e.g., projectionscreens or backlit displays.

In connection with the preferred use of the device according to theinvention for guiding sunlight into a room, preferably in buildings, oneobjective is to miniaturize the structures necessary for guiding light,not least for const considerations. So-called optical near-field effectsthat cannot be described by laws of geometric optics become importantwhen miniaturizing such surface structures. When sunlight hits suchmicrostructures, which typically have structural dimensions of 100 μm orless, preferably less than 20 μm, diffraction-induced near-field effectsexplainable by interference effects arise, the effective manifestationof which depends very heavily on the angle of incidence of the sunlighthitting the microstructures.

Such microstructures, whose effect and configuration are described,among other places, in DE 100 28 426 A1, are just as advantageouslysuitable for use as structural surfaces for guiding and/or scatteringlight, which can be utilized either in combination with the macroscopic,optically active surface structures, wherein the macroscopic, opticallyactive surface structures are in this case provided with the near-fieldeffect-inducing microstructures either over their entire surface or onlyin specific surface areas, or are applied in place of the macroscopic,optically active surface structures onto a surface upper side, at leastin partial areas. Precisely these microstructure surfaces are coveredaccording to the invention at least in partial areas of their surfacewith an optically switchable layer, whose optical effect on the sunlightpassing through the microstructure surface is significantly influencedby the near-field effects induced by the microstructures. It isparticularly advantageous to provide only those areas of themicrostructure with the optically switchable layer on which especiallyhigh near-field intensities arise for specific angles of incidence atwhich sunlight hits the microstructure surface.

The microstructure surface completely coated with a light-induced,optically switchable layer, preferably consisting of photochromicmaterial, could be locally tinted at locations of higher near-fieldintensity, which can indeed result in optically interesting phenomena.

In addition, further studies of the device according to the inventionhave surprisingly shown that, aside from optically switchable coatingmaterials, optically active layers whose absorption, transmission and/orreflection behavior is independent of time, i.e., chronologicallyinvariable, as is the case for dielectric or metallic layer materials,for example, exhibit comparably good optical light guiding or scatteringproperties, as can be observed when using the device according to theinvention described above, provided the optically active layers are usedat least in combination with a microstructure surface.

In a second alternative approach, a light guiding device consisting ofat least one partially translucent material with a surface upper side istherefore designed in such a way that the surface upper side providesoptically active surface structures for guiding and/or scattering light,wherein at least partial areas of the optically active surfacestructures provide microstructures covered at least partially with anoptically active layer, which utilizes near-field effects induced by themicrostructures for its optical effect.

It was surprisingly shown that the danger of glare could be kept low onthe one hand, while on the other hand influencing the solar radiationflux in such a way as to avoid overheating in warm times of the year andensure a marked supply of warmth in cold times of the year.

Similarly surprisingly good results could also be achieved by having thesurface upper side of the surface material be provided exclusively witha microstructure surface, i.e., without the additional provision ofmacroscopic surface structures. In this case, the microstructures are atleast partially covered with an optically active layer, which utilizesnear-field effects induced by the microstructures for its opticaleffect.

The coating is only of special importance for the advantageous opticaleffect of the microstructured surface upper side in those surface areasof the microstructures where intensity maximums and minimums in the nearfield arise during exposure to light. Only upper edge progressions ofthe microstructures are preferably covered by the optically activelayer, e.g., one designed as a thin metal layer and having constantreflection and absorption properties. The use of dielectric layershaving specific, constant transmission properties is basicallyconceivable as well.

As already briefly touched upon above, microstructures are indeed alsotaken to mean differently shaped, geometric microstructure elementsmeasuring 100 μm in size, preferably less than 20 μm, and a preferredaspect ratio of greater than 0.2.

Typical three dimensional microstructure elements respectively raisedover the surface upper side include prismatic, square, parabolic,convexly or concavely curved or pyramidal structural elements, whosestructural dimensions trigger interference effects when correspondinglyexposed to sunlight that result in field modulations in the near fieldon the order of the wavelength of the light incident on themicrostructures. It was shown that a pivotal influence can be exerted onnear field formation via the locally limited coating of microstructureflanks or edges, preferably with a metal layer. Such microstructuresexhibit a very high angular dependence relative to the light incident onthe microstructures in terms of its optical deflection behavior. Themasking behavior depending on the angle of incidence can be set in ahighly precise manner with respect to the optical deflection capacity ofthe microstructures via the suitable, selective coating ofmicrostructure flanks or edges.

The developing near field effects can also influence the transmissionproperties of the entire translucent surface element wavelength-selectively as a function of the angle of incident of the lighthitting the microstructures. As a result, suitably coating themicrostructure makes it possible to introduce a targeted downwardadjustment of transmission behavior for sunlight from the longer-wavespectrum at high angles of incidence of the kind encountered duringsummertime in our latitude to prevent overheating inside of rooms, whilesimultaneously ensuring that long-wave radiation can pass through thesurface material virtually intact at the flat angles of incidenceencountered in our latitude during cold times of the year.

The inventive combination of a device having microstructures opticallyactive at least in partial areas with a selective coating made ofoptically active material that is not necessarily optically switchablerepresents a device for use preferably as a shading element, whichmerges the advantages recognized at the outset in prior art whileavoiding it disadvantages.

In addition to the proposed use for the selective, local coating ofmicrostructures with an optically active layer, which exerts adielectric or absorbing effect, and has reflection, transmission and/orabsorption properties independent of time, it is of course also possibleto use optically switchable layer materials of the kind proposed inconjunction with the first alternative solution described above.

All known optically switchable materials are essentially suitable forthe light guiding device according to the invention. Without callinginto question the fundamental suitability of remaining materials, thelayer materials especially preferred from the group of opticallyswitchable layer materials with electrochromic, photochromic,phototropic, photoelectrochromic, thermochromic, thermotropic orgasochromic switching properties based on present knowledge forrealizing the device according to the invention are gasochromic.Particularly suitable for this purpose are transitional metal oxides,e.g., tungsten oxide, tungstates, nioboxide, molybdenum oxide,molybdates, nickel oxide, titanium oxide, vanadium oxide, iridium oxide,manganese oxide, cobalt oxide or mixtures of the aforementioned oxidetypes. Also suitable as gasochromic materials are metal hydrides, e.g.,La_(1-z)Mg_(z)H_(x), Y_(1-z)Mg_(z)H_(x), Gd_(1-z)Mg_(z)H_(x), Yh_(b),LaH_(b), SmH_(b), NiMg₂H_(x), CoMg₂H_(x) or mixtures thereof, with zvalues in the 0 to 1 range, x values in the 0 to 5 range, and b valuesfrom 0 to 3, or switchable polymers, such as polyviologens,polythiophenes or polyanilines, or Prussian Blue.

Layer thicknesses of between 100 nm to 100 nm are selected in the caseof the transitional metal oxides described above for planar or limitedplanar deposition onto the corresponding surfaces. Particularly suitablelayer thicknesses measure 200 to 600 nm. However, if the gasochromiclayer material is selected from the group of metal hydrides, layerthicknesses of between 10 nm and 500 nm, preferably between 20 nm up to50 nm, are already sufficient. The latter material class is preferablysuitable for selectively coating the smallest surface sections on themicrostructures, in which only the corner passages or specificallyaligned lateral flank surfaces relative to the incident light arecovered by just a think layer.

In order to improve the switchability of the gasochromic layer materialsdescribed above, the layer materials are combined with catalyticmaterials. Such catalytic materials include platinum, iridium,palladium, rhodium osmium, rhenium, nickel, ruthenium or mixtures of theaforementioned metal types. The catalysts designed as layers preferablyexhibit preferred layer thicknesses of 10 nm or less, preferably of 3nm.

The use of gasochromic layers in combination with light guiding orscattering surface structures has the following advantages, inparticular for selectively coating specific areas of the surfacestructure:

-   -   The layer structure is particularly simple. Especially during a        selective coating of specific areas of the surface structure,        this greatly simplifies coating outlay relative to complex        multi-layer systems.    -   Gasochromic layer systems generally combine a comparatively        thick gasochromic layer, e.g., a transitional metal oxide        typically 100 nm to 1000 nm thick, preferably 200 nm to 600 nm,        with a thin catalyst layer, typically thinner than 10 nm,        preferably thinner than 3 nm.    -   Selective application to specific areas of the surface structure        can readily be performed using deposition methods, e.g., vapor        depositing or sputtering, in which the layer particles expand in        a straight line, thereby producing a shading effect. Limiting        the angular range of these layer particles during the deposition        process makes it possible to readily achieve a selective coating        of the surface structure, as will be described further later on.        However, this is generally also associated with a reduction in        the effective deposition rate. Gasochromic layer systems provide        a good opportunity to apply the thick, gasochromic layer in a        planar manner, and apply the thin catalyst layer selectively,        thereby generating a coating that switches only in the areas        with the catalyst. The disadvantage to the reduced deposition        rate for the catalyst layer is then not serious, since very thin        layers are sufficient here anyway.    -   A gasochromic coating selectively deposited in specific areas        can be switched just as easily as a planar coating via flooding        with reactive gases. In layer systems requiring electrical        contacting, e.g., electrochromic, the switching outlay can rise        unequally given selective coating.    -   To protect the optically active surface structures, it is often        also necessary to embed them in an intermediate space in the        pane between two substrates. This intermediate space in the pane        is then also available to be flooded with reactive gases of the        kind required for gasochromic layers.    -   Similarly, cavities of the kind generated by putting together        two complementary structures can be equipped inside with        gasochromic layers, and then flooded with reactive gases.

In like manner, the aforementioned gasochromic material classes aresuitable as electrochromic layer materials, and must in this case onlybe hooked up to an electrical control potential for switching theiroptical transmission behavior, and not be exposed to a targeted gasflow, as in the gasochromic operating mode.

Liquid crystals are not particularly suitable if selectively determinedareas of the surface structure are to be made switchable, since it isvery difficult to encapsulate them over selective areas. In particularif the one electrode surface of a liquid crystal system is applied tolarger structural depths, it may become necessary to incline the secondone parallel to the first one, which becomes very complicated. The useof liquid crystals on large surfaces is basically complicated andexpensive.

Much the same holds true for the application of “suspended particledevices” (SPD). Phototropic and thermotropic materials requirecomparatively large layer thicknesses (typically greater than 10 μm or100 μm), many organic photochromic materials of the kind used insunglasses typically greater than 1 μm. As a result, they are notparticularly well suited, in particular for selectively coating specificstructural areas.

By contrast, those optically switchable systems having thin layers withthicknesses under 10 μm, preferably less than 1 μm, are well suited.Examples of these include gasochromic, electrochromic,photoelectrochromic, photochromic or thermochromic layer systems. Suchphotoelectrochromic layer systems are described, for example, in “Newphotoelectrochromic device”, Electrochimica Acta, Volume 46, Issues13-14, Apr. 2, 2001, pp. 2131-2136, A.

Hauch, A. Georg, S. Baumgaertner, U. Opara Krasovec and B. Orel, or in“User controllable photochromic (UCPC) devices”, Electrochimica Acta,Volume 44, Issue 18, May 1, 1999, pp. 3017-3026, Gimtong Teowee, ToddGudgel, Kevin McCarthy, Anoop Agrawal, Pierre Allemand and John Cronin.Suitable photochromic and photoelectrochromic systems are described inDE 198 16 675 A1, for example. Thin thermochromic layer systems includeVO2, e.g., doped with tungsten or molybdenum (see “Thermochromic glazingof windows with better luminous solar transmittance”, Solar EnergyMaterials and Solar Cells, Volume 71, Issue 4, Mar. 1, 2002, pp.537-540, Moon-Hee Lee).

Of the switchable systems described above, several cannot be switched ina controlled manner, i.e., they react passively to external influences,in particular temperature (thermochromic, thermotropic) and luminousintensity (photochromic, phototropic). In comparison to these, theactively controllable systems (e.g., gasochromic, electrochromic,photoelectrochromic) offer the advantage that they can be influenced toa greater degree.

A series of alternative coating techniques are suitable formanufacturing the device according to the invention, whose opticallyactive surface structures, whether they assume macroscopic ormicroscopic dimensions, are provided with either locally selective layerdeposits, whether they be optically switchable or static.

Known vapor depositing or sputtering processes in which the individualcoating particles expand along a straight line on the surface to becoated are suitable. Therefore, inclined coating makes it possible toselectively coat those lateral flanks of the surface structures facingthe respective coating source, while the lateral surfaces facing awayfrom the coating source or shaded from other structures remain uncoated.

Sputtering processes are typically executed under an argon atmosphereand with pressure conditions under which the average free path length ofthe gas particles is less than or roughly the same as the distance fromthe sputtering source (target) to the substrate, so that the sputteringparticles can be expected to scatter. By contrast, if high-mass sputterparticles like tungsten or platinum are selected, and a light sputteringgas like helium or neon is additionally used, the heavy sputteringparticles can expand nearly along a straight line, and formflank-selective coatings on geometric structures. In addition, it isadvantageous to use suitably applied masks during the sputtering processif the objective is to only expose specific angular regions for coatingpurposes relative to the straight line along which the sputteringparticles expand. However, much the same thing can be accomplished byinclining the target or substrate, e.g., using rollers for guiding inthe case of a film coating.

Wet chemical coating methods are also conceivable, such as immersion,spraying, centrifuging, doctoring or pressing, but the surfacestructures to be coated must be preprocessed in a first step in such away that only selective flank areas are coated via wet chemicaldeposition as the entire surface structure is brought into contact withthe coating material. This is achieved by having certain structuralsurface areas exhibit hydrophilic, hydrophobic, lipophilic or lipophobicsurface properties. These surface properties can also be generated bysmall structures, i.e., structures smaller than 10 μm. If the structuresare held to less than the length of a light wave, i.e., less than 400nm, their influence on the optical properties is not that great in thearea of the solar radiation. For example, they can be transferred to afilm substrate surface via mechanical embossing. Depending on thecomposition of the coating solutions, selective flank coatings can begenerated in this way.

Also conceivable are combinations of various coating methods, forexample the combined application of vapor deposition or sputtering, aswell as wet chemical methods. A sputtering process can be used toselectively deposit separating layers on limited substrate surfaces. Inan ensuing wet chemical method, for example, an optically switchablelayer is applied over the entirety of the surface substrate. As theseparating layer is then detached, the optically active layer cansubsequently be locally removed, leaving the optically active layer onlyon the remaining surface areas.

The opposite also holds true, as the entire surface upper side furnishedwith optically active surface structures can be coated with an opticallyactive layer, for example, and then covered selectively with a blockinglayer. This blocking layer can prevent the switching function in thecase of an optically switchable layer as the optically active layer, andgreatly impair its optical properties in the case of a static layer.

In optically switchable multi-layer systems, e.g., a thicker gasochromiclayer combined with a thinner catalyst layer, it is also possible toseparate only one layer selectively, e.g., the thinner layer, and havethe remaining layers over the entire surface, so that the switchingfunction is only present at locations where all individual layers arepresent.

Other suitable methods include those in which the coating is influencedby an illumination of the structured surface, and layer deposition takesplace, for example, precisely at locations with a higher or lowerluminous intensity. Possible examples of this are the process ofpolymerizing out monomers under UV illumination or illuminatingphotoresist structures with subsequent development and, if necessary,additional coating and/or liftoff processes.

BRIEF DESCRIPTION OF THE INVENTION

The invention will be described by example below based on exemplaryembodiments making reference to the drawing, without limiting theoverall inventive idea. Shown on:

FIG. 1 a to d are cross sectional views of a window element in which thedevice configured according to the invention is used for guiding light;

FIG. 2 is a window element with optically active surface structures andmicrostructures;

FIG. 3 a-e is a window element thermotropic layer material, and on

FIG. 4 a, b, c are views showing the ray progression through a windowelement with thermotropic layer material.

WAYS FOR IMPLEMENTING THE INVENTION, COMMERCIAL APPLICABILITY

The light guiding device described above comprised of at least onepartially translucent surface material is advantageously suited forintegration into a window element, which will be described in detaildrawing reference to the following exemplary embodiments.

FIG. 1 a shows a diagrammatic cross section through a double-glazedwindow element, which is bordered on both sides by opposing window glasspanes 1 and 4. Provided within the gap between the windowpanes 1 and 4is the surface material 2 designed as a kind of glass pane, the leftsurface upper side of which in the figure provides macroscopic surfacestructures 21. The surface structures 21 each have three lateral flanks,of which one is oriented parallel to the back side of the surfacematerial 2.

The three lateral flanks in the exemplary embodiment shown on FIG. 1along with the glass pane 2 enclose a cavity 22, which is enveloped bythree optically active interfaces, which essentially determine theoptical deflection capacity for the sunlight incident on the windowelement into the interior of a room.

The exemplary embodiment according to FIG. 1 a assumes that glass pane 1is the outer pane, and glass pane 4 is the inner pane of a windowelement. Provided between the structured pane 2 and the inner pane 4 isan optically switchable layer system 3, e.g., consisting of an opticallyswitchable layer and a catalyst, e.g., WO₃ and platinum. The pane cavity22 can be filled alternately with a reducing gas, e.g., diluted H₂, andan oxidizing gas, e.g., diluted 02, as a result of which the layerbecomes colored or discolored, e.g., in the case of WO₃ and platinum.Additional details relating to such an optically switchable system mayalso be gleaned from DE 44 40 572.

The optically switchable layer system 3 acts to reduce the glare effectof the geometric structure 21, which results from the production processowing to the lack of edge configurations (keyword edge rounding).

FIG. 1 b shows an exemplary embodiment in which an optically switchablelayer 3 is provided over the entirety of the surface structure of thesurface material 2. By contrast, FIG. 1 c shows an embodiment in whichonly specific flanks of the surface structure 21 are provided with anoptically switchable coating 3. The structural dimensions can bemacroscopic, e.g., greater than 100 μm, or microscopic, e.g., less than100μ.

Such a structure can be manufactured, for example, by embossing alight-guiding structure in a plastic film. The latter is thenselectively coated with a gasochromic layer via vapor deposition orsputtering, after which the film is applied to the inside of a doubleglazed pane. Typical structural can be periodic prisms with atranslucent area, as sketched on FIG. 1, wherein individual flanksand/or edge roundings are selectively coated. Typical structuraldimensions here range between 10 and 50 μm, for example.

FIG. 1 d provides a detailed view of a manufacturing-induced edgerounding, which can lead to undesired glare effects. However,specifically coating the edge area with the optically switchable layer 3makes it possible to effectively reduce the glare effects caused byrounding.

Particularly advantageous combinations also result from light-guidingsurface structures and photochromic layer materials. Photochromic layermaterials typically discolor on exposure to light, so that in particularthose layer areas become tinted that are exposed to a high luminousintensity. For example, light-guiding structures with a correspondinggeometric design make it possible to guide direct sunlight to specificlocations of the photochromic layer, thereby inducing localdiscolorations, while the photochromic layer at other remainstranslucent at other locations, for example. The opposite reaction isalso conceivable in principle, i.e., a photochromic material thatdiscolors during exposure to light, but otherwise remains tinted orreflective.

FIG. 2 shows an exemplary embodiment of a window element comparable tothe drawing on FIG. 1 c, but the surface element 2 incorporated betweenthe windowpanes 1 and 4 has microstructures 5, on which an opticallyactive layer 31 is applied not necessarily designed as an opticallyswitchable layer is applied, also only in partial areas. Themicrostructures 5 on FIG. 2 are greatly magnified to improve visibility.

Locally limited areas of the microstructures 5, preferably themicrostructure edge progressions, are provided with metal coatings 31,which are able to influence the near field effects induced by themicrostructures 5 during irradiation in a specific way, and hencedetermine the light deflection capacity of the entire window element.

The provision of microstructures 5 according to the exemplary embodimenton FIG. 2 essentially makes it possible to realize a sharp angularselectivity, i.e., the light is reflected back during exposure to directsunlight and with the sun in a high position over the horizon, as occursprimarily in the summer, while the light is allowed through at low sunpositions, mainly in the winter. Wavelength selectivity can essentiallyalso be achieved. This affords protection against overheating in thesummer while simultaneously making use of the sunlight to heat up thebuilding in winter. At the same time, deflecting the direct sunlight,e.g., to the ceiling of the interior space during winter with the sun inlow positions makes it possible to avoid glare.

The microstructures also provide for a near field that by nature dependsmuch more on wavelength than the optical function of macroscopicstructures, in which geometric optics determine the effect, whichideally is independent of wavelength.

With respect to protection against overheating, it is advantageous tomask out, or best reflect, the non-visible region, in particular thenear infrared region, of the sunlight, but allow the visible regionthrough to illuminate the interior space. The inventive combination ofmicrostructures and optically active layers permits sharper wavelengthselectivity, a lower absorption and the use of simpler layers, e.g.,single layers, such as metals, while placing less demand on thesubstrate.

FIG. 3 a to 3 e show additional variants for a light-guiding system,which can be integrated into window elements, preferably window elementswith dual glazing, similarly to the exemplary embodiments drawingreference to FIG. 1 a-d.

FIG. 3 a shows a diagrammatic cross section through a multi-layer windowstructure, which provides a thermotropic composite panel 6 arranged asthe outer pane a distance away from an inner pane 4 designed as aprismatic glazing. In this case, the thermotropic composite panel 6consists of three layers, wherein a thermotropic material is heldbetween two glass panes otherwise transparent to sunlight. Particularlysuited for use as the glass pane facing the prismatic glazing 7 is aso-called Low-e layer 8, which consists of a material that radiateslittle thermal radiation. The prismatic glazing 7 preferably consists ofan inner pane 4 transparent to normal sunlight, with a surfacestructured film 21 applied thereto. A gas space is enclosed between theLow-e layer 8 and the film 21.

As an alternative to the embodiment shown on FIG. 3 a, the exemplaryembodiment according to FIG. 3 b also makes it possible to notencapsulate the thermotropic material on both sides by glass panes orthe like, but rather to provide the prismatic glazing 7 immediatelyopposite on a composite layer comprised of an outer pane 1 transparentto sunlight and a Low-e layer 8 applied thereto.

FIG. 3 c to d provide further configuration variants. On FIG. 3 c, theoptically switchable layer 3 preferably consisting of thermotropicmaterial is self-contained between the composite layer comprised of theouter pane 1 and Low-e layer 8, as well as the inner pane 4 providedwith the structured surface 21. On FIG. 3 d, the outer pane 1 is spacedapart from the optically switchable layer 3, which is applied directlyto the structured surface 21. On FIG. 3 e, the outer pane 1 directlycontacts the optically switchable layer 3, which is applied to thestructured surface 21 as on FIG. 3 d.

The thermotropic composite windowpanes described above make it possibleto use suitable thermotropic materials to indicate a completelyautonomously operating light guiding system, which allows warmingradiant flux to pass into the room in winter, while avoiding overeatingeffects in summertime. This is because, as opposed to the transmissionbehavior of conventional thermotropic materials, which are transparentwhen cold and diffusely scattering when warm, use is made of specificthermotropic materials with the opposite transmission behavior, i.e.,diffusely scattering when cold, and largely transparent to sunlight whenwarm, as is the case, for example for paraffins or other latent storagematerials, such as salt solutions, yielding the radiation situationsshown on FIGS. 4 a and b.

Assuming on FIG. 4 a that cold temperatures predominate, i.e., inparticular in wintertime, at which the thermotropic layer materialassumes a turbid or diffuse state, diffusely scattering incidentsunlight in the direction of the prismatic glazing 7. In particular, theprismatic glazing 7 is designed in such a way as to be largelyreflective for high solar altitudes in the summer, while transmitting atlower solar altitudes, in particular during wintertime. Since theintroduction of solar rays into a room is desired at wintertimetemperatures, as described in the above case, the diffuse scattering oflight on the thermotropic material layer 3 nearly precludes thereflection effect of the prismatic glazing 7, so that the solarradiation flux can get inside the room largely unimpeded (FIG. 4 a).This stands in contrast with the situation at higher temperatures thatpredominate during summertime according to the depiction on FIG. 4 b. Inthis case, heating causes the thermotropic layer material 3 to assumetransparent properties, as a result of which the sunlight streaming infrom outside hits the light-guiding surface structures of the prismaticglazing 7 virtually unscattered. At a suitably high solar altitude, onlyrays of the sun that hit the prismatic glazing at a specific angle areguided inside the room. The far higher share of rays is reflected backby the prismatic glazing 7 as a result of its prismatic function (asshown on FIG. 4 c).

REFERENCE LIST

-   1 Outer pane-   2 Structured surface material-   21 Surface material-   22 Cavity-   3 Optically switchable layer-   31 Optically active layer-   4 Inner pane-   5 Microstructure-   6 Thermotropic composite panel-   7 Prismatic glazing-   8 Low-e layer

1. A device for guiding light consisting of at least one partially translucent surface material, with a surface upper side, which has optically active surface structures for guiding and/or scattering light, as well as an optically switchable coating provided at least in partial areas of the surface structures, or at least two directly or indirectly opposing surface upper sides, of which one exhibits optically active surface structures for guiding and/or scattering light, and the other provides an optically switchable coating that covers at least parts of the surface upper side.
 2. The device according to claim 1, characterized in that the optically active surface structures at least in partial areas provide microstructure surfaces that are covered at least in part by an optically switchable layer, which uses near-field effects triggered by the microstructures and based on diffraction and interference effects for their optical effect.
 3. The device according to claim 1, characterized in that the optically active surface structures are designed as microstructures.
 4. The device for guiding light consisting of at least one partially translucent surface material, with a surface upper side, which has optically active surface structures for guiding and/or scattering light, which at least in partial areas provide microstructure surfaces that are covered at least in part by an optically active layer, and use near-field effects triggered by the microstructures and based on diffraction and interference effects for their optical effect, or a surface upper side, which has a microstructure surface for guiding and/or scattering light, which is covered at least in part by an optically active layer, and uses near-field effects triggered by the microstructures for their optical effect.
 5. The device according to claim 2, characterized in that the microstructures exhibit average structural periods of less than 100 μm in size, preferably less than 20 μm, and an aspect ratio, i.e., ratio of structural height to structural period, of greater than 0.2.
 6. The device according to claim 4, characterized in that the optically active layer is applied exclusively to areas on the microstructure surface where excessively higher or lower near field intensities arise on the microstructure surface, i.e., intensity maximums and minimums generated on the microstructure surface owing to diffraction and interference effects, at specific angles of incidence for light relative to the surface upper side
 7. The device according to claim 4, characterized in that the optically active layer has absorption, transmission and/or reflection behavior is independent of time.
 8. The device according to claim 4, characterized in that the optically active layer is an optically switchable layer.
 9. The device according to claim 1, characterized in that the optically switchable layer is selectively applied to specific areas of the surface structure.
 10. The device according to claim 1, characterized in that the optically switchable layer is thinner than 10 μm, preferably thinner than 1 μm.
 11. The device according to claim 1, characterized in that the optically switchable layer exhibits gasochromic, electrochromic, photochromic, photoelectrochromic or thermochromic layer material.
 12. The device according to claim 1, characterized in that the switching function of the optically switchable layer can be actuated.
 13. The device according to claim 12, characterized in that the optically switchable layer exhibits a gasochromic, electrochromic or photoelectrochromic layer material.
 14. The device according to claim 11, characterized in that the gasochromic layer material is selected from the following material classes: transitional metal oxides, e.g., tungsten oxide, tungstates, nioboxide, molybdenum oxide, molybdates, nickel oxide, titanium oxide, vanadium oxide, iridium oxide, manganese oxide, cobalt oxide or mixtures thereof, metal hydrides, e.g., La_(1-z)Mg_(z)H_(x), Y_(1-z)Mg_(z)H_(x), Gd_(1-z)Mg_(z)H_(x), Yh_(b), LaH_(b), SmH_(b), NiMg₂H_(x), CoMg₂H_(x) or mixtures thereof, with z values in the 0 to 1 range, x values in the 0 to 5 range, and b values from 0 to 3, or switchable polymers, such as polyviologens, polythiophenes or polyanilines, or Prussian Blue.
 15. The device according to claim 14, characterized in that the layer material consists of transitional metal oxides having a layer thickness ranging from 100 nm to 1000 nm, preferably 200 nm to 600 nm, or metal hydrides with a layer thickness ranging from 10 nm to 500 nm, preferably 20 nm to 50 nm.
 16. The device according to claim 11, characterized in that the gasochromic layer material is actively connected with catalytic material.
 17. The device according to claim 16, characterized in that the catalytic material is designed as a type of layer, and contains platinum, palladium, rhodium, osmium, rhenium, nickel, ruthenium or mixtures thereof.
 18. The device according to claim 17, characterized in that the catalytic layer has a layer thickness of less than 10 nm, preferably less than 3 nm.
 19. The device according to claim 1, characterized in that the optically switchable layer exhibits phototropic or thermotropic layer material.
 20. The device according to claim 19, characterized in that the optically switchable layer is applied at least to partial areas of a surface upper side, and spaced indirectly or directly apart from the surface upper side provided with optically active surface structures for guiding and/or scattering light.
 21. The device according to claim 20, characterized in that the optically switchable layer is incorporated between two surface elements transparent to sunlight.
 22. The device according to claim 19, characterized in that the thermotropic layer material is diffusely scattering when cold, and largely transparent when warm.
 23. The device according to claim 22, characterized in that the thermotropic layer material contains paraffins or latent storage material, such as salt solutions.
 24. The device according to claims 11, characterized in that the electrochromic layer material can be selected from the material classes: transitional metal oxides, e.g., tungsten oxide, tungstates, nioboxide, molybdenum oxide, molybdates, nickel oxide, titanium oxide, vanadium oxide, iridium oxide, manganese oxide, cobalt oxide or mixtures thereof, metal hydrides, e.g., La_(1-z)Mg_(z)H_(x), Y_(1-z)Mg_(z)H_(x), Gd_(1-z)Mg_(z)H_(x), Yh_(b), LaH_(b), SmH_(b), NiMg₂H_(x), CoMg₂H_(x) or mixtures thereof, with z values in the 0 to 1 range, x values in the 0 to 5 range, and b values from 0 to 3, or switchable polymers, such as polyviologens, polythiophenes or polyanilines, or Prussian Blue.
 25. The device according to claim 1, characterized in that the optically active surface structures are given macroscopic geometries rising vertically to the surface upper side of the surface material or take the form of cuts or recesses in the surface material, and exhibit interfaces at which light is refracted or diffracted according to the laws of geometric optics.
 26. The device according to claim 1, characterized in that at least partially translucent surface material consists of at least one carrier substrate transparent to sunlight resembling a massive pane.
 27. The device according to claim 1, characterized in that the partially translucent surface material is a window element, preferably for buildings, or part of a window element.
 28. The device according to claim 1, characterized in that the partially translucent surface material takes the form of a single carrier substrate transparent to sunlight, with the optically active surface structures and the optically switchable layer or the microstructure surfaces optically active in the near field range with the optically active layer on a respective shared surface upper side or on respective different surface upper sides.
 29. The device according to claim 1, characterized in that two carrier substrates transparent to sunlight are provided, whose surface upper sides are spaced apart opposite each other, that the optically active surface structures on one of the two opposing surface upper sides and the optically switchable layer or the microstructure surfaces optically active in the near field on the opposing surface upper side are provided with the optically active layer.
 30. The device according to claim 29, characterized in that the two carrier substrates transparent to sunlight are designed as windowpanes of a dual glazing, whose opposing surface upper sides incorporate that intermediate space of the panes.
 31. The device according to claim 1, characterized in that the at least partially translucent surface material is designed as a kind of film.
 32. The device according to claim 21, characterized in that the film is attached to a carrier substrate transparent to sunlight.
 33. The device according to claim 1, characterized in that the optically active surface structures are geometrically uniform and, based on the presumption of a prescribed periodic sequence, are formed and arranged on the surface upper side, and that the optically switchable layer is applied to all surface structures over their entire surface, or only selectively to specific partial areas of the surface structures.
 34. The device according to claim 33, characterized in that an optically non-switchable layer with absorption, transmission and/or reflection properties not dependent on time is selectively applied in other areas of the surface structures in combination with an optically switchable layer selectively applied in specific partial areas of the surface structures.
 35. The device according to claim 1, characterized in that the surface structures exhibit corners or edges that are locally coated with an optically switchable or optically active layer with absorption, transmission and/or reflection properties not dependent on time. 